A giant Mekong catfish captured by a dai fishery in Cambodia's lower Tonle Sap river on October 21, 2002. The dais, or bag-nets, are large cone-shaped nets that catch fish as they move out of the Tonle Sap Lake into the Tonle Sap River and the mainstream of the Mekong.
PHOTO COURTESY OF ZEB HOGAN
A dam being constructed downstream on the Mekong River will pose a new threat to a giant catfish species with an already dwindling population, according to a study commissioned by the World Wildlife Fund (WWF).
The Xayaburi Dam, which Laos began construction on last year amid controversy, will present an "impassable" barrier for the migratory catfish that can reach up to three meters in length and 300 kilograms in weight, the organization quoted the study as saying in a press release.
It will put the species, one of the world's largest and rarest freshwater fish, on brink of extinction, it said.
With its size, the fish will not be able to swim across such a large barrier to reach its spawning area further upstream, said Dr. Zeb Hogan, associate research professor at the University of Nevada, who authored the study.
The new dam could disrupt and even block spawning and increase the mortality rate of the fish, if they have to pass through dam turbines, the study claims.
"These river titans need large, uninterrupted stretches of water to migrate, and specific water quality and flow conditions to move through their lifecycles of spawning, eating and breeding," Hogan said.
According to WWF, PÃ¶yry, the Finnish firm advising Laos on the dam's construction, once said that "fish passages" could be built to allow fish to pass through turbines unencumbered, but such passages "have never been successfully put into place."
Dr. Eric Baran with the World Fish Center was quoted as saying that "fish ladders" cannot work without builders understanding the species being targeted, including their swimming capabilities in relation to the river's currents.
"Research is still needed to ensure mitigation efforts will work," Baran said.
According to the study's findings, the Mekong's giant catfish were once widely dispersed throughout the river basin, possibly as far as Myanmar and southwestern China.
They were "relatively abundant" up until the early 1900s when their population started plummeting, due to over-fishing and the destruction of their habitat due to dams built along the river's tributaries, it said.
For example, in the Mun River in Thailand, the largest Mekong tributary, a dam already blocks the migration of the species and has isolated the river from the remainder of the Mekong basin.
Although the catfish's population is not known exactly, there could be as few as a couple hundred adult fish left in the river and its tributaries in Cambodia, Laos and Thailand, it said.
The study cited catch figures as evidence of the fish's "steep decline." It said the numbers dropped from thousands in the late 1880s to dozens in the 1990s, and down to only a few in recent times.
The species is still fished illegally and caught accidentally in fisheries targeting other species although a ban is already in place in Thailand and Cambodia, while Laos also has laws to regulate fishing activities pertaining to the catfish species.
Hogan urged the countries' authorities to monitor catches to protect the species from being fished illegally.
"Key measures" to prevent the giant species from disappearing, according to the study, include urgent efforts to safeguard its critical habitat and migratory corridors, and increased international cooperation, such as basin-wide management.
In a call to protect the fish, Dr. Lifeng Li, Director of WWF's Global Freshwater Program, called the species' status "an indicator of the health of the entire river."
"The Mekong giant catfish can be saved, but it will take a level of commitment from all lower Mekong countries, as well as international organizations and donors, that currently do not exist," he said.
Last September, Laos started work on the Xayaburi Dam, which was estimated to cost US$3.5 billion, although members of the Mekong River Commission a regional body established to coordinate dam projects on the river agreed to delay a decision on its construction in 2011.
The project has faced widespread criticism related to serious gaps in data and failures to fully account for the impact the dam will have, especially on fisheries and sediment flows, WWF said.
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